CN113637830A - Method for accelerating sigma phase nucleation and growth of high-carbon austenitic heat-resistant steel - Google Patents
Method for accelerating sigma phase nucleation and growth of high-carbon austenitic heat-resistant steel Download PDFInfo
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- 238000001816 cooling Methods 0.000 claims abstract description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 16
- 229910000734 martensite Inorganic materials 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 5
- 238000005480 shot peening Methods 0.000 claims description 4
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- 239000010935 stainless steel Substances 0.000 claims description 3
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2201/00—Treatment for obtaining particular effects
- C21D2201/03—Amorphous or microcrystalline structure
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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Abstract
The invention discloses a method for accelerating sigma phase nucleation and growth of high-carbon austenitic heat-resistant steel, which comprises the following steps: s1, shot blasting is carried out on the high-carbon austenitic heat-resistant steel, and a plastic deformation layer is formed on the surface; s2, carrying out aging treatment on the sample treated in the step S1, and carrying out water cooling; wherein the temperature of the aging treatment is 620-680 ℃; the time of the aging treatment is 12-240 h. According to the invention, the nanocrystalline structure of the supercritical saturated deformation value is prepared on the surface of the sample through a surface nanocrystallization technology, and finally the violent plastic deformation nano-layer sample with a certain thickness is subjected to aging treatment at a specific temperature, so that the nucleation and growth of the sigma phase of the high-carbon austenitic heat-resistant steel are remarkably accelerated, the problem that the early-stage sigma phase sample is difficult to obtain is solved, and the deep research and understanding of the micro-behavior mechanism of the sigma phase are facilitated.
Description
Technical Field
The invention relates to the field of austenite heat-resistant steel failure and protection, in particular to a method for accelerating sigma phase nucleation and growth of high-carbon austenite heat-resistant steel.
Background
The thermal power generation accounts for more than 70% of the power generation distribution in China and occupies the leading position of an energy structure. The development of advanced thermal power generating units can improve the thermal power generation efficiency, is more beneficial to improving the current environmental pollution problem, and is a necessary trend of the thermal power generation technology development. Because the high-carbon austenitic heat-resistant steel has excellent high-temperature mechanical property and structure stability, the high-carbon austenitic heat-resistant steel becomes an important manufacturing material for parts of supercritical thermal power generating units in recent years in China. Under high-temperature service, the precipitated phase in the Super304H is mainly M23C6Nb (C, N) and Cu-rich are equal. In addition, the sigma phase may be precipitated at each stage of the service cycle of the austenitic heat-resistant steel, and is a brittle and hard phase which has a great influence on the heat-resistant steel and is generally closely related to the service life of the austenitic heat-resistant steel.
The occurrence of sigma phase reduces the toughness of a matrix, weakens the creep resistance and intergranular corrosion resistance of the high-carbon austenitic heat-resistant steel, is easy to induce stress corrosion cracking to cause explosion, and is an important influence factor for reducing the service safety of the heat-resistant steel. Most of the events of the austenitic heat-resistant steel which is damaged and failed are related to the sigma phase, so that the improvement of a sigma phase detection method and a service life safety evaluation mechanism according to the precipitation characteristics is urgently needed.
Compared with other precipitated phases, the precipitation of the sigma phase in the high-carbon austenitic heat-resistant steel is more difficult, the precipitation is possible only after long-time high-temperature service, and the sigma phase is found in the 304H steel under the high-temperature condition for more than ten years in the related art, but if a certain technical method is adopted, the nucleation and the growth of the sigma phase in the austenitic heat-resistant steel can be accelerated only within 24 hours. Meanwhile, as the microscopic behavior mechanism of the sigma phase is not clear, in the related art, it is generally difficult to obtain a research sample containing the early sigma phase in a short time, and only the sigma phase can be researched from the retired or failed austenitic heat-resistant steel, but at this time, the mechanism of the precipitation behavior of the sigma phase cannot be deeply understood.
Therefore, it is required to develop an aging treatment method of high carbon austenitic heat-resistant steel, which can accelerate the nucleation and growth of sigma phase of high carbon austenitic heat-resistant steel.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an aging treatment method of high-carbon austenitic heat-resistant steel, which can accelerate the sigma phase nucleation and growth of the high-carbon austenitic heat-resistant steel.
The invention provides a method for accelerating sigma phase nucleation and growth of high-carbon austenitic heat-resistant steel, which comprises the following steps;
s1, shot blasting is carried out on the high-carbon austenitic heat-resistant steel, and a plastic deformation layer is formed on the surface;
s2, carrying out aging treatment and water cooling on the product treated in the step S1;
wherein the temperature of the aging treatment is 620-680 ℃;
the time of the aging treatment is 12-240 h.
The invention provides a method for preparing a nanocrystalline structure with a supercritical saturated deformation value on the surface of high-carbon austenitic heat-resistant steel by utilizing a surface nanocrystallization technology, and a violent deformation nano-layer structure is prepared by combining specific temperature aging treatment, so that the nucleation and growth of sigma phase in the austenitic heat-resistant steel are remarkably accelerated. The method has the advantages of short treatment time, high treatment efficiency, saving of a large amount of time, contribution to deep research of sigma-phase microscopic behavior mechanism, and great significance for improving service safety and service life evaluation of the austenitic heat-resistant steel.
According to some embodiments of the invention, the plastically deformable layer:
the surface grain size is less than or equal to 28 nm.
According to some embodiments of the invention, the plastically deformable layer:
the volume content of martensite is more than or equal to 15 percent.
According to some embodiments of the invention, the plastically deformable layer:
the thickness is more than or equal to 110 mu m.
According to some embodiments of the invention, the shot peening process of step S1 includes the steps of: putting the high-carbon austenitic heat-resistant steel into an efficient shot blasting machine to perform shot blasting treatment on the surface of a sample;
wherein the time required for 100 percent of the surface coverage is 1 min-2 min.
According to some embodiments of the present invention, the high-efficiency blasting machine has a nozzle moving in a zigzag back-and-forth uniform motion.
According to some embodiments of the present invention, the shot peening process in step S1,
the distance between a nozzle and the surface of the high-carbon austenitic heat-resistant steel is as follows:
60mm～100mm；
according to some embodiments of the invention, the high efficiency peening machine peens are one of cast steel balls and stainless steel balls.
According to some embodiments of the invention, the high-efficiency peening machine comprises the following process parameters: the pressure of the shot blasting air is 0.3 Mpa-0.8 Mpa.
The shot blasting pressure is too low to meet the supercritical saturation requirement, and the effect cannot be produced even through the aging treatment at the specific temperature. On the other hand, too high a shot pressure can lead to fatigue failure of the material.
According to some embodiments of the invention, when the peening air pressure is 0.3MPa or less, the peening duration is > 15 min.
According to some embodiments of the invention, the peening duration is > 5min when the peening air pressure is > 0.3 Mpa.
According to some embodiments of the invention, the high carbon austenitic heat resistant steel has a carbon mass fraction of 0.05% to 0.25%.
According to some embodiments of the invention, the high carbon austenitic heat resistant steel comprises one of Super304H, 304H and S347H.
According to some embodiments of the invention, the high carbon austenitic heat resistant steel is subjected to a grinding and polishing treatment;
the grinding and polishing treatment comprises the following process parameters:
and sequentially using sand paper with different meshes to grind the surface of the high-carbon austenitic heat-resistant steel, and then polishing by using a grinding paste.
According to some embodiments of the present invention, the coated abrasive has a grit number of 200-2000 grit.
According to some embodiments of the invention, the abrasive paste is diamond.
According to some embodiments of the invention, the abrasive paste has a mesh size of 5000 mesh.
The invention has at least the following beneficial effects:
according to the invention, the nanocrystalline structure of the supercritical saturated deformation value is prepared on the surface of the sample through a surface nanocrystallization technology, and finally the violent plastic deformation nano-layer sample with a certain thickness is subjected to aging treatment at a specific temperature, so that the nucleation and growth of the sigma phase of the high-carbon austenitic heat-resistant steel are remarkably accelerated, the problem that the early-stage sigma phase sample is difficult to obtain is solved, and the deep research and understanding of the micro-behavior mechanism of the sigma phase are facilitated. Meanwhile, the time cost is greatly shortened, the sigma phase detection method of the high-carbon austenitic heat-resistant steel is perfected, the establishment of a high-carbon austenitic heat-resistant steel service life evaluation mechanism is facilitated, the reduction of creep resistance and corrosion resistance of the high-carbon austenitic heat-resistant steel caused by hidden danger sigma phase in the future is prevented, explosion caused by stress corrosion cracking is avoided, and casualty accidents and social and economic losses are finally reduced.
Drawings
FIG. 1 is a graph showing the thickness of a severe plastic deformation layer of a surface-nanocrystallized sample in example 1 and example 2 of the present invention;
FIG. 2 is a graph showing the thickness of a severe plastic deformation layer at different shot blasting times of 0.6MPa in the test example of the present invention;
FIG. 3 is a graph showing the average grain size and martensite content at different shot blasting times of 0.6MPa in the test examples of the present invention;
FIG. 4 is an image of the microstructure of an aged sample in example 1 of the present invention;
FIG. 5 is an image of the microstructure of an aged sample in example 2 of the present invention;
FIG. 6 is an image of the microstructure of an aged sample in example 3 of the present invention;
FIG. 7 is an image of the microstructure of an aged sample in example 4 of the present invention;
FIG. 8 is a graph of hardness at different depths of 650 ℃ for example 1 of the present invention;
FIG. 9 is an image of the microstructure of an aged sample in example 3 of the present invention;
FIG. 10 is an image of the microstructure of an aged sample in example 4 of the present invention;
FIG. 11 is an image of the microstructure of an aged sample in example 5 of the present invention;
FIG. 12 is an image of the microstructure of an aged sample in example 6 of the present invention.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
The high-carbon austenitic heat-resistant steel selected in the embodiment of the invention is Super304H steel pipe with specification phi of 45mm multiplied by 9mm (diameter multiplied by thickness), and the chemical composition of the steel is shown in table 1.
TABLE 1 Super304H Steel pipe with various component contents
| Element(s) | C | Mn | Si | P | S | Cr | Ni | Cu | Nb | N | Mo |
| Measured value | 0.091 | 0.69 | 0.21 | 0.030 | 0.005 | 18.20 | 8.52 | 3.11 | 0.49 | 0.08 | 0.22 |
Example 1
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
s1, selecting a heat treatment device: a high-temperature box type industrial resistance furnace and a cooling water tank;
s2, selecting an efficient shot blasting machine with the measuring range of 0.8Mpa and a stainless steel ball with the diameter of 0.6 mm;
s3, polishing:
a flat block-like sample was cut from a supplied Super304H heat-resistant steel, and the size of the sample was 45mm (length) X28 mm (width) X5 mm (height). And then grinding the cut square sample by using 200-mesh sand paper, cooling the water by using the sand paper in the grinding process, and continuously replacing 320-mesh, 500-mesh, 800-mesh and 2000-mesh sand papers for carrying out the same operation until the surface of the square sample is not obviously changed. Polishing the ground sample to a flat mirror surface state by using 5000-mesh diamond grinding paste, finally washing the surface by using absolute ethyl alcohol, and drying the sample by using a blower;
s4, surface nanocrystallization:
after grinding and polishing, the square sample is put into a high-efficiency shot blasting machine and fixed by a steel clamp. Then setting the air pressure of the high-efficiency shot blasting machine to be 0.6Mpa, and enabling the nozzle to continuously and uniformly move the Z shape of the surface of the sample back and forth for 14min at a position 80mm away from the surface of the sample, namely covering the surface of the sample with shot blasting for 14 times. Finally, obtaining a supercritical saturated deformation nano-layer with a certain thickness on the surface of the sample to obtain a surface nanocrystallized sample;
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 650 ℃, putting the surface nanocrystallized sample into an effective heating area of the resistance furnace, and heating and preserving heat for 24 hours to obtain an aged sample; then the sample after aging treatment is immersed in a water tank for rapid cooling to obtain a 0.6Mpa-14min nanocrystallization + 650-24 h aging treatment sample.
Example 2
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 1 in that:
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 650 ℃, putting the surface nanocrystallized sample into an effective heating area of the resistance furnace, and heating and preserving heat for 168 hours to obtain an aged sample; then the sample after aging treatment is immersed in a water tank for rapid cooling, and the aging treatment sample of 0.6Mpa-14min nanocrystallization + 650-168 h is obtained.
Example 3
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 2 in that:
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 620 ℃, putting the surface nanocrystallized sample into an effective heating zone of the resistance furnace, and heating and preserving heat for 168 hours to obtain an aged sample; and then, immersing the sample subjected to aging treatment in a water tank for rapid cooling to obtain a 0.6Mpa-14min nanocrystallization + 620-168 h aging treatment sample.
Example 4
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 2 in that:
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 680 ℃, putting the surface nanocrystallized sample into an effective heating zone of the resistance furnace, and heating and preserving heat for 168 hours to obtain an aged sample; and then immersing the sample subjected to aging treatment in a water tank for rapid cooling to obtain a 0.6Mpa-14min nanocrystallization + 680-168 h aging treatment sample.
Example 5
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 1 in that:
this example does not use the surface nanocrystallization treatment, i.e., does not perform step S4 in example 1;
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 650 ℃, putting the supplied sample into an effective heating area of the resistance furnace, and heating and preserving heat for 96 hours to obtain an aged sample; and then immersing the aged sample into a water tank for rapid cooling to obtain an aged sample with a common supply state of + 650-96 h.
Example 6
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 1 in that:
s4, surface nanocrystallization:
after grinding and polishing, the square sample is put into a high-efficiency shot blasting machine and fixed by a steel clamp. Then setting the air pressure of the high-efficiency shot blasting machine to be 0.6Mpa, and enabling the nozzle to continuously and uniformly move the Z shape of the surface of the sample back and forth for 2min at a position 80mm away from the surface of the sample, namely covering the surface of the sample with shot blasting for 2 times. Finally, obtaining a supercritical saturated deformation nano-layer with a certain thickness on the surface of the sample to obtain a surface nanocrystallized sample;
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 650 ℃, putting the surface nanocrystallized sample into an effective heating area of the resistance furnace, and heating and preserving heat for 168 hours to obtain an aged sample; then the sample after aging treatment is immersed in a water tank for rapid cooling to obtain a 0.6Mpa-2min nanocrystallization + 650-168 h aging treatment sample.
Example 7
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 1 in that:
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 450 ℃, putting the surface nanocrystallized sample into an effective heating zone of the resistance furnace, and heating and preserving heat for 168 hours to obtain an aged sample; and then immersing the sample subjected to aging treatment in a water tank for rapid cooling to obtain a 0.6Mpa-14min nanocrystallization + 450-168 h aging treatment sample.
Example 8
The embodiment is a method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel, which comprises the following steps:
this example differs from example 1 in that:
s5, aging treatment:
heating a high-temperature box type industrial resistance furnace to 700 ℃, putting the surface nanocrystallized sample into an effective heating zone of the resistance furnace, and heating and preserving heat for 168 hours to obtain an aged sample; and then immersing the sample subjected to aging treatment in a water tank for rapid cooling to obtain a 0.6Mpa-14min nanocrystallization + 700-168 h aging treatment sample.
Test example:
the test example is to test the thickness curve, the grain size curve and the martensite content curve of the severe deformation layer of the surface nanocrystallization treatment process at different shot blasting times under 0.6Mpa, and calculate the grain size and the martensite content.
The performance test method of the samples prepared in the embodiments 1 to 6 of the invention is as follows:
measuring the thickness of the severe plastic deformation layer of the surface nanocrystallized sample:
s1, performing electrolytic corrosion on the vertical section of the surface nanocrystallized sample by using an oxalic acid solution with the mass fraction of 10%, wherein the specific electrolytic parameters of the direct current power supply are as follows: the current density is 0.15A/cm2～0.40A/cm2The voltage is 5V-6V;
s2, observing the vertical section of the electrolyzed and corroded nanocrystallized sample by using a metallographic microscope, wherein austenite grains are covered, and calculating the thickness of the severe plastic deformation layer of the sample by software.
Grain size and martensite content measurement: and calculating the grain size and the martensite content according to the thickness curve, the grain size curve and the martensite content curve of the severe deformation layer at different peening times under 0.6 Mpa.
And (3) metallographic structure observation: vilella reagent (1 gC ratio) was used6H3N3O7+5mL HCl+100mL C2H5OH) corroding two 650 ℃ aging treatment sample tissues for 80s, washing and drying the sample tissues by tap water and absolute alcohol in sequence after corrosion, and observing the metallographic structures of the sample by using an optical microscope.
Vilella reagent (1 gC ratio) was used6H3N3O7+5mL of HCl (38% by mass) +100mL of C2H5OH) to corrode two 650 ℃ aging-treated sample tissues, wherein the time required for corrosion is 80S, and tap water and anhydrous water are used after corrosionThe alcohol is washed and dried in sequence, and then the metallographic structure of the sample is observed by using an optical microscope.
The results of the test of the thickness of the severe plastic deformation layer of the surface nanocrystallized sample in the embodiment 1 and the embodiment 2 of the present invention are shown in fig. 1, and it is known from fig. 1 that the thickness of the severe plastic deformation layer of the surface nanocrystallized sample is 126 μm, and if the thickness is more than or equal to 110 μm, the thickness requirement of the plastic deformation layer is satisfied.
The results of measuring the thickness curve of the severe deformation layer, the size of the crystal grain and the martensite content in the test example of the present invention are shown in table 2.
TABLE 2 results of measurements of thickness of severe deformation layer, grain size and martensite content in test examples of the present invention
| Shot blasting time | Thickness of severe deformation layer (μm) | Grain size (nm) | Martensite content (%) |
| 2min | 40 | 34.5 | 5 |
| |
110 | 28.7 | 10.5 |
| |
120 | 27 | 17 |
| 11min | 123 | 26.2 | 19.5 |
| 14min | 126 | 25.7 | 21 |
| 17min | 132 | 25 | 24 |
| 20min | 137 | 24 | 26.7 |
The results of the measurements of the thickness curve, the grain size and the martensite content of the severe deformation layer in the test example of the invention are shown in fig. 2 and fig. 3: combining the data in fig. 2 and fig. 3, when the shot blasting time is 14min, the average grain size of the surface of the sample is 25.7nm, the martensite content is 21%, and the supercritical saturated deformation requirement is met.
When the shot blasting time is 2min, the thickness of the severe plastic deformation layer of the sample is 40 μm, the average grain size is 34.5nm, the martensite content is 5%, and the supercritical saturated deformation requirement is not met.
The gold phase diagrams of the aging treatment samples of the examples 1 and 2 are shown in fig. 4 and 5, and it is shown in fig. 4 and 5 that the aging treatment samples of the examples 1 and 2 have different degrees of sigma phase precipitation, which shows that the sigma phase of the austenitic heat-resistant steel Super304H can be rapidly shown in short 24 hours (shown in fig. 4) after the surface nanocrystallization and the specific temperature aging treatment (shown in fig. 5), and the sigma phase in the heat-resistant steel Super304H can continuously grow with the increase of the aging time (shown in fig. 5).
The gold phase diagrams of the aging samples of the examples 3 and 4 of the invention are shown in fig. 6 and 7, and it is known from fig. 6 and 7 that the samples prepared in the examples 3 and 4 also have obvious sigma phase precipitation, but compared with the sample prepared in the example 2, the sigma phase content and the precipitation speed are smaller, so 650 ℃ is the optimal aging temperature of the invention.
In addition, the hardness does not change significantly with the aging time at 650 ℃ (as shown in fig. 8), which shows that the surface nanocrystalline structure can be well maintained at the temperature.
The gold phase diagrams of the aging samples of the examples 5 and 6 of the present invention are shown in fig. 9 and 10, and it can be seen from fig. 9 and 10 that the aging samples of the examples 5 and 6 of the present invention have no sigma phase precipitation, indicating that the samples cannot develop the sigma phase in a short time without the surface nanocrystallization (see fig. 9). On the other hand, if the degree of nanocrystallization is low, it is difficult for the sample to obtain a nanolayer of supercritical saturated strain, and even if the aging time is much longer than that of the sample in example 1, the sigma phase cannot be developed (as shown in fig. 10).
Referring to fig. 11 and 12, it can be seen from fig. 11 and 12 that the gold phase diagrams of the aging samples of examples 7 and 8 of the present invention show that the samples of examples 7 and 8 of the present invention have no sigma phase precipitation, which indicates that if the set aging temperature does not meet the aging requirement at a specific temperature (about 650 ℃), the samples cannot rapidly develop the sigma phase in a short time (as shown in fig. 11 and 12).
The following results were obtained by combining the test results of embodiments 1 to 8 of the present invention: by a surface nanocrystallization technology, a nanocrystalline structure with a supercritical saturated deformation value is prepared on the surface of the high-carbon austenitic heat-resistant steel Super304H, and the nucleation and growth of a sigma phase in the austenitic heat-resistant steel can be remarkably accelerated by combining with a violent deformation nanocrystalline structure with a certain thickness through aging treatment at a specific temperature. The low-strength surface nanocrystallization can only generate common plastic deformation, cannot introduce high-energy over-deformation sites, and is difficult to nucleate sigma phase, while the high-strength surface nanocrystallization can exceed the fatigue life of heat-resistant steel to damage the heat-resistant steel, so that the surface nanocrystallization treatment needs to meet the requirement of supercritical saturated deformation. Meanwhile, the aging treatment temperature is too low, the total energy of the nanocrystalline structure cannot exceed the sigma phase transition energy barrier, and the sigma phase is difficult to nucleate; and the temperature of the aging treatment is too high, the supercritical saturated deformation nanocrystalline structure is easy to recrystallize, the average grain size is also grown, and the sigma phase is prevented from appearing in a short time, so that the aging treatment temperature of 650 ℃ is more favorable for the nucleation and growth of the sigma phase.
Aiming at the problems that a hidden danger sigma phase microscopic behavior mechanism in high-carbon austenitic heat-resistant steel, an important manufacturing material of a supercritical thermal power generating unit part, is unclear, an early sample is difficult to obtain and the like, a nanocrystalline structure with a supercritical saturated deformation value is prepared on the surface of the material through a surface nanocrystallization technology, and then a violent deformation nano-layer structure with a certain thickness is subjected to aging treatment at a specific temperature, so that the sigma phase is promoted to nucleate and grow at a high-energy crystalline phase interface and a chromium segregation area, and a rapid and convenient way is finally provided for deeply understanding the sigma phase microscopic behavior mechanism and perfecting a high-carbon austenitic heat-resistant steel service life evaluation mechanism.
In conclusion, the method prepares the nanocrystalline structure with the supercritical saturated deformation value on the surface of the sample through the surface nanocrystallization technology, and finally treats the violent plastic deformation nano-layer sample with a certain thickness through the aging treatment at a specific temperature, so that the nucleation and the growth of the sigma phase of the high-carbon austenitic heat-resistant steel are remarkably accelerated, the problem that the early sample of the sigma phase is difficult to obtain is solved, and the deep research and understanding of the micro-behavior mechanism of the sigma phase are facilitated. Meanwhile, the time cost is greatly shortened, the sigma phase detection method of the high-carbon austenitic heat-resistant steel is perfected, the establishment of a high-carbon austenitic heat-resistant steel service life evaluation mechanism is facilitated, the reduction of creep resistance and corrosion resistance of the high-carbon austenitic heat-resistant steel caused by hidden danger sigma phase in the future is prevented, explosion caused by stress corrosion cracking is avoided, and casualty accidents and social and economic losses are finally reduced.
While the embodiments of the present invention have been described in detail with reference to the description and the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the gist of the present invention within the knowledge of those skilled in the art. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.
Claims (10)
1. A method for accelerating the nucleation and growth of sigma phase of high-carbon austenitic heat-resistant steel is characterized by comprising the following steps: the method comprises the following steps:
s1, shot blasting is carried out on the high-carbon austenitic heat-resistant steel, and a plastic deformation layer is formed on the surface;
s2, carrying out aging treatment and water cooling on the sample treated in the step S1;
wherein the temperature of the aging treatment is 620-680 ℃;
the time of the aging treatment is 12-240 h.
2. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 1, wherein: the plastic deformation layer:
the grain size is less than or equal to 28 nm;
preferably, the plastic deformation layer: the volume content of martensite is more than or equal to 15 percent;
preferably, the plastic deformation layer: the thickness is more than or equal to 110 mu m.
3. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 1, wherein: the shot peening process in step S1 includes the steps of: putting the high-carbon austenitic heat-resistant steel into an efficient shot blasting machine, and carrying out shot blasting treatment on the surface of a sample;
wherein the time required for 100 percent of the surface coverage is 1 min-2 min.
4. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 3, wherein: the shot peening in the step S1,
the distance between a nozzle and the surface of the high-carbon austenitic heat-resistant steel is as follows: 60 mm-100 mm;
5. the method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 3, wherein: the high-efficiency shot blasting machine is used for blasting shot of one of cast steel balls and stainless steel balls.
6. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 3, wherein: the high-efficiency shot blasting machine comprises the following process parameters: the pressure of the shot blasting air is 0.3 Mpa-0.8 Mpa.
7. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 6, wherein: when the pressure of the shot blasting air is less than or equal to 0.3Mpa, the shot blasting duration is more than 15 min.
8. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 6, wherein: when the pressure of the shot blasting air is more than 0.3Mpa, the duration of shot blasting is more than 5 min.
9. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 1, wherein: the high-carbon austenitic heat-resistant steel contains 0.05-0.25% of carbon by mass.
10. The method for accelerating the nucleation and growth of sigma phase of high carbon austenitic heat resistant steel according to claim 9, wherein: the high-carbon austenitic heat-resistant steel comprises one of Super304H, 304H and S347H.
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| CN114959191A (en) * | 2022-05-09 | 2022-08-30 | 燕山大学 | Method for improving corrosion resistance of super austenitic stainless steel by regulating sigma phase |
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